Vehicles may include cooling systems configured to reduce overheating of an engine by transferring the heat to ambient air. Therein, coolant is circulated through the engine block to remove heat from the hot engine, and the heated coolant is then circulated through a radiator near the front of the vehicle. Heated coolant may also be circulated through a heat exchanger to heat a passenger compartment. The flow of coolant through the various vehicle system components is controlled based on a coolant temperature sensed at a thermostat.
One example approach for cooling system control is shown by Ap et al. in US 2005/0000473. Therein, a main coolant line is interconnected with one or more secondary coolant loops through the use of various bypasses and valves. A position of the valves, and accordingly a flow of coolant through the engine system is based at least on an engine loading state. Specifically, when engine loading is low, and engine cooling is not a priority, coolant is diverted from the main line to the secondary loops, to assist in secondary component cooling.
However, the inventors herein have identified potential issues with such an approach. As one example, since coolant flow through the various cooling system components is affected by the coolant temperature sensed at the thermostat, even if the engine is bypassed, the coolant temperature impinging on the thermostat may be high and coolant temperature regulation in the main line may initiate. The resulting regulated temperature of coolant in the main line may be cooler than a regulated coolant temperature required for higher engine performance.
In one example, some of the above issues may be at least partly addressed by a method for an engine cooling system, comprising, responsive to an engine operating condition, adjusting each of a bypass shut-off valve and a heater shut-off valve of the cooling system to stagnate a first amount of coolant at an engine block while circulating a second amount of coolant at a thermostat. In this way, by adjusting the various cooling system valves, a volume of coolant as well as a source of coolant circulating at the thermostat may be varied, thereby varying a coolant temperature affected at the thermostat.
As an example, during an engine cold-start, one or more valves of a cooling system may be closed to vary an amount of coolant stagnating at the engine block, while also varying an amount of coolant circulating at the thermostat. For example, a bypass shut-off valve in a first bypass loop between the engine and the thermostat may be closed to stagnate coolant at the engine block. Additionally, or optionally, a heater shut-off valve in a second heater loop between the engine and the thermostat, downstream of a heater core, may be closed to stagnate coolant at the engine and heater core.
As such, the relatively smaller amount of stagnating coolant at the engine block may assist in expediting engine warm-up during the engine cold-start. The relatively larger amount of coolant circulating and sensed at the thermostat may then be used to regulate the coolant temperature. For example, a relatively higher regulated temperature may be achieved by closing the bypass shut-off valve and opening the heater shut-off valve since the thermostat may sense an oil cooler outlet temperature. In contrast, a relatively lower regulated temperature may be achieved by closing the heater shut-off valve and opening the bypass shut-off valve since the thermostat may sense a cylinder head coolant temperature.
In this way, by selectively exposing a thermostat to heated coolant from a different region of the cooling system, the actual resulting coolant temperature at a point of temperature measurement (e.g., via an ECT or CHT sensor) can be affected and controlled. In other words, the cooling system's regulating coolant temperature limit may be controlled. By doing so, a variable and controllable engine coolant temperature may be achieved by using the existing set of cooling system valves. By allowing the engine temperature to vary from a temperature sensed at the thermostat, engine performance benefits may be achieved during selected operating conditions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.